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A simulation-based large deflection and inelastic analysis of steel frames under fire

Chi Kin Iu, Siu Lai Chan

Department of Civil and Structural Engineering , The Hong Kong Polytechnic University, Kowloon, Hong Kong

Received 15 July 2003, Revised 20 February 2004, Accepted 12 March 2004


This paper presents an accurate and robust geometric and material nonlinear formulation to predict structural behaviour of unprotected steel members at elevated temperatures. A fire analysis including large displacement effects for frame structures is presented. This finite element formulation of beam–column elements is based on the plastic hinge approach to model the elasto-plastic strain-hardening material behaviour. The Newton–Raphson method allowing for the thermal-time dependent effect was employed for the solution of the nonlinear governing equations for large deflection in thermal history. A combined incremental and total formulation for determining member resistance is employed in this nonlinear solution procedure for the efficient modeling of nonlinear effects. Degradation of material strength with increasing temperature is simulated by a set of temperature–stress–strain curves according to both ECCS and BS 5950 Part 8, which implicitly allows for creep deformation. The effects of uniform or non-uniform temperature distribution over the section of the structural steel member are also considered. Several numerical and experimental verifications are presented.


Fire engineering; Large deflection analysis; Inelastic analysis

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